13 359 



mpr= +12-239+r008(m— 12) — -017 (m— 12)^ 



where ritpr is the provisional magnitude and m the definitive one. 



The correction of nipr to m is tlierefore zero at 8°'"5 and 16'"'0. Its maximum 

 value between tliese two magnitudes is — "^'24 for nipr = 12'2. There will however 

 still remain systematic differences between stars near to and far from the centre of 

 the plates. Near the border of the field bright stars have probably been estimated 

 too bright, and faint ones too faint. The magnitudes are therefore supposed to be 

 most reliable for stars less than 40' distant from Alcyone. For this region I find 

 bj' comparison with the magnitudes of A. X. 4767 the mean error to be about ±""'1 

 at 14™ and about ±'"'2 at 15"\ Especially the faintest magnitudes are therefore 

 uncertain even in the central region of the field investigated, but they are only 

 meant to serve for Durchmusterung purposes. 



7. The Coordinates. 



The coordinates were noted to the tenth of a mm and converted into « and 

 Ô for 1900 for the following plates 53, 78, 105, 125, 127, 144, 146, 147, 243, 244, 

 245, 246, 247, 248, 305, 306, 307 and 312. The coordinates of a few stars not oc- 

 curring on these plates have been added separately. For stars less than 40' distant 

 from Alcyone the mean error is in both coordinates about ziz 2". For stars near the 

 border of the field investigated it may be double this amount. This will be suffi- 

 cient for the identification of the stars. 



8. Spectra of the ir^ Order. 



For the reduction of the effective wavelengths derived from the spectra of the 

 II"'' order to normal intensitj' of the image I have not made use of the diameter d 

 of the central star image, but the intensity of the spectra of the 11°'' order them- 

 selves was directly estimated on the plate. These estimates were made by estimating 

 the diameter d' of the central star image for which the spectra of the P' order would 

 have the same intensity as that actually observed for the spectra of the II"'' order. 

 With these equivalent diameters d' I then proceeded exactly in the same way as 

 above with the diameter d referring to the spectra of the P' order. The approximate 

 relation between d and d', which for the rest is of no importance, is in the mean 



d = -24 -30 -36 -42 mm 



d'=-084 -089 -100 •121mm. 



When the diameter d of the central image is small, the spectra of the II"'' 

 order could only be measured when the air was quiet and the images consequently 



